Implantable medical device conductor insulation and process for forming

ABSTRACT

An elongate medical electrical lead conductor includes a layer of hydrolytically stable polyimide formed thereover.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/909,518 filed on Aug. 2, 2004 and entitled “IMPLANTABLE MEDICALDEVICE CONDUCTOR INSULATION AND PROCESS FOR FORMING”, which is acontinuation-in-part of U.S. patent application Ser. No. 10/407,653filed on Apr. 4, 2003 and entitled “IMPLANTABLE MEDICAL DEVICE CONDUCTORINSULATION AND PROCESS FOR FORMING”, which claims priority and otherbenefits from U.S. Provisional Patent Application Ser. No. 60/371,995,filed Apr. 11, 2002, entitled “BIO-STABLE IMPLANTABLE MEDICAL DEVICELEAD CONDUCTOR INSULATION AND PROCESS FOR FORMING”, all of which areincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical deviceleads for delivering therapy, in the form of electrical stimulation, andin particular, the present invention relates to conductor coilinsulation in implantable medical device leads.

BACKGROUND OF THE INVENTION

Implantable medical electrical leads are well known in the fields ofcardiac stimulation and monitoring, including neurological stimulationand cardiac pacing and cardioversion/defibrillation. In the field ofcardiac stimulation and monitoring, endocardial leads are placed througha transvenous route to position one or more sensing and/or stimulationelectrodes in a desired location within a heart chamber orinterconnecting vasculature. During this type of procedure, a lead ispassed through the subclavian, jugular, or cephalic vein, into thesuperior vena cava, and finally into a chamber of the heart or theassociated vascular system. An active or passive fixation mechanism atthe distal end of the endocardial lead may be deployed to maintain thedistal end of the lead at a desired location.

It is highly desirable that implantable leads have the lowest possibleprofile while the insulation maintain sufficient integrity toelectrically isolate one or more conductors of the leads over the lifeof the implanted lead.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of theinvention and therefore do not limit its scope, but are presented toassist in providing a proper understanding of the invention. Thedrawings are not to scale (unless so stated) and are intended for use inconjunction with the explanations in the following detailed description.Embodiments of the present invention will hereinafter be described inconjunction with the appended drawings, wherein like numerals denotelike elements, and:

FIG. 1 is a schematic diagram of an exemplary implantable medical devicein accordance with one embodiment of the present invention;

FIG. 2 is a cross-sectional view of a lead of the exemplary device takenalong cross-sectional lines II-II of FIG. 1;

FIG. 3 is a cross-sectional view of the lead of the exemplary devicetaken along cross-sectional lines of FIG. 1;

FIG. 4 is a cross-sectional view of a coiled wire conductor forming afilar of a multi-filar conductor coil according to one embodiment of thepresent invention;

FIG. 5 is a cross-sectional view of a coiled wire conductor forming afilar of a multi-filar conductor coil according to another embodiment ofthe present invention; and

FIG. 6 is a cross-sectional view of an exemplary cabled wire conductoraccording to yet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of an exemplary implantable medical devicein accordance with one embodiment of the present invention. Asillustrated in FIG. 1, an implantable medical device 100 according tothe present invention includes an implantable medical device lead 102and an implantable medical device housing 104, such as an implantablecardioverter/defibrillator or pacemaker/cardioverter/defibrillator(PCD), for example, for processing cardiac data sensed through lead 102and generating electrical signals in response to the sensed cardiac datafor the provision of cardiac pacing, cardioversion and defibrillationtherapies. A connector assembly 106 located at a proximal end 101 oflead 102 is insertable within a connector block 120 of housing 104 toelectrically couple lead 102 with electronic circuitry (not shown) ofhousing 104.

Lead 102 includes an elongated lead body 122 that extends betweenproximal end 101 and a distal end 121 of lead 102. An outer insulativesheath 124 surrounds lead body 122 and is preferably fabricated ofpolyurethane, silicone rubber, a fluoropolymer or a combination thereof.Coiled wire conductors in accordance with one embodiment of the presentinvention are positioned within lead body 122, as will be described indetail below. Distal end 121 of lead 102 includes a proximal ringelectrode 128 and a distal tip electrode 126, separated by an insulativesleeve 130. Proximal ring electrode 128 and distal tip electrode 126 areelectrically coupled to connector assembly 106 by one or more coilconductors, or filars extending between distal end 121 and proximal end101 of lead 102 in a manner shown, for example, in U.S. Pat. Nos.4,922,607 and 5,007,435, incorporated herein by reference in theirentireties.

FIG. 2 is a cross-sectional view of a lead of the exemplary device takenalong cross-sectional lines II-II of FIG. 1. As illustrated in FIG. 2,lead 102 of implantable medical device 100 includes a quadrafilarconductor coil 200 including four individual filars, or coiled wireconductors 202A, 202B, 202C and 202D extending within insulative sheath124 of lead body 122. Coiled wire conductors 202A-202D electricallycouple proximal ring electrode 128 and distal tip electrode 126 withconnector assembly 106. It is understood that although the presentinvention is described throughout in the context of a quadrafilarconductor coil, having each of two electrodes electrically coupled to aconnector assembly via two of the four individual coiled wireconductors, the present invention is not intended to be limit toapplication in a quadrafilar conductor coil. Rather, the lead conductorinsulator of the present invention can be utilized in any conductorconfiguration, including the use of any number of conductor coilsdepending upon the number of desired electrodes, and would include theuse of a single filar electrically coupling the electrode to theconnector. Furthermore, as illustrated in FIG. 6, a lead conductoraccording to an alternate embodiment of the present invention may be inthe form of a cable 630 including a plurality of bundled wire strands632-638.

FIG. 3 is a cross-sectional view of the lead of the exemplary devicetaken along cross-sectional lines of FIG. 1. As illustrated in FIGS. 2and 3, each of the individual filars or coiled wire conductors 202A,202B, 202C and 202D are parallel-wound in an interlaced manner to have acommon outer and inner coil diameter. As a result, conductor coil 200forms an internal lumen 204, which allows for passage of a stylet orguide wire (not shown) within lead 102 to direct insertion of lead 102within the patient.

Alternately, lumen 204 may house an insulative fiber, such as ultrahighmolecular weight polyethylene (UHMWPE), liquid crystal polymer (LCP),polyester and so forth, or an insulated cable (i.e. cable 630illustrated in FIG. 6) in order to allow incorporation of an additionalconductive circuit and/or structural member to aid in chronic removal oflead 102 using traction forces. Such an alternate embodiment wouldrequire insertion and delivery of lead 102 to a final implant locationusing alternate means, such as a catheter, for example. Lumen 204 mayalso include an insulative liner (not shown), such as a fluoropolymer,polyimide, PEEK, for example, to prevent damage caused from insertion ofa style/guidewire (not shown) through lumen 204.

FIG. 4 is a cross-sectional view of a coiled wire conductor forming amulti-filar conductor coil according to some embodiments of the presentinvention. As illustrated in FIG. 4, one or more of the individualcoiled wire conductors 202A, 202B, 202C and 202D includes a conductorwire 210 surrounded by an insulative layer 212. According to the presentinvention, insulative layer 212 is formed of a hydrolytically stablepolyimide, such as a Soluble Imide (SI) polyimide material, for example,(formerly known as Genymer, Genymer SI, and LaRCT™ SI) as described inU.S. Pat. No. 5,639,850, issued to Bryant, and incorporated herein byreference in its entirety, to insulate conductor coils in implantablemedical device leads. Such SI polyimide material is currentlycommercially available through license from NASA, for example. Thethickness of the insulative layer 212 ranges from approximately 0.0001inches up to approximately 0.0050 inches, forming a corresponding wallthickness W of the insulative layer 212. By utilizing the hydrolyticallystable polyimide material as an insulative layer 212, the presentinvention provides an improved electrically insulating material that ishydrolytically stable in implantable (in vivo) applications.

According to one embodiment of the present invention, the insulativelayer 212 is applied onto the conductor wire 210 in multiple coats, thatis, layer 212 is comprised of multiple layers of a hydrolytically stablepolyimide resulting in a desired wall thickness W. The coating isapplied in such a way to provide a ductile, robust insulative layer thatenables a single filar, i.e., coiled wire conductor, or multiple filar,i.e., coiled wire conductors, to be wound into a single wound conductorcoil 200 of sizes ranging from an outer diameter D (FIG. 3) of 0.010inches to 0.110 inches. For example, the coating process includes asolvent dip followed by an oven cure cycle to drive off the solvents andcolumn 7, line 63 to column 8, line 14 of U.S. Pat. No. 4,056,651, whichis incorporated herein by reference, describes a coating procedure whichmay be employed to manufacture embodiments of the present invention.According to an exemplary embodiment, wire 210, having a diameterbetween approximately 0.003 inch and approximately 0.005 inch, afterbeing cleaned with an alkaline solution, undergoes 32 coating passesresulting in wall thickness W of approximately 0.0005 inch. For thisembodiment the inventors have found that, in order to assure an adequatetoughness and flexibility of each imidized coating layer, that is toprevent cracking upon subsequent processing of the coated wire, eachlayer should be exposed to a high enough temperature, for example anoven temperature between approximately 650° F. and approximately 850°F., for a sufficient time to drive off residual solvent. Thus, multiplecoating passes forming insulative layer 212 on conductor wire 210provides the ductility that is needed to make the coated conductor wire210 into a conductor coil 200 that can withstand the long term flexrequirements of an implantable lead. However, according to an alternateembodiment, one or more wire filars may be wound into a coiledconfiguration prior to applying a layer or layers of a hydrolyticallystable polyimide. The inventors further contemplate spraying processesand extrusion processes known to those skilled in the art may also beemployed to manufacture embodiments of the present invention.

The use of the hydrolytically stable polyimide insulative layer 212according to embodiments of the present invention offers an exceptionaldielectric strength for electrical insulation. Through flex studies onconductor coils coated with the SI polyimide, the inventors have foundthat the insulative layer 212 also has high flex properties in regardsto stimulating lead conductor coil flex testing. The SI coating invarious wall thicknesses will remain intact on the coil filar until thecoil filar fractures as seen in conventional conductor coil flex studies(reference 10 million to 400 million flex cycles at various 90 degreeradius bends).

Conductor coils 200 (FIG. 2) according to the present invention caninclude a single filar or multiple filars, with each filar being anindividual circuit that could be associated with a tip electrode, a ringelectrode, a sensor, and so forth. The present invention enables the useof multiple circuits in a single conductor coil, resulting in adownsizing of the implantable medical device. For example, there isapproximately a 40 to 50 percent reduction in lead size between knownbipolar designs, which traditionally utilized an inner coil and innerinsulation, outer coil and outer insulation, to a lead design havingmultiple circuits in a single conductor coil having the insulative layer212 according to the present invention.

Hydrolytically stable polyimides do not show a notable decrease inmechanical performance over time when immersed in an aqueousenvironment, such as an implant environment. Examples of polyimidesconsidered to be hydrolytically stable may have the following generalrecurring structure:

Wherein AR is either AR1 or AR2 that represent different dianhydridesand wherein either AR1 or AR2 is represented by the following generalformula including isomeric variations thereof:

Wherein X can be represented by CH₂, CH₃—C—CH₃, O (Oxygen), C═O(carbonyl), S (sulfide), SO₂ (sulfonyl), CF₃—C—CF₃ (hexafluoropropanederivative), or no element (e.g., 3,4,3′4′-biphenyltetracarboxylicdianhydride (BPDA)) and wherein AR3 is a diamine and can be representedby the following formula:

including, as shown below, isomeric variations thereof:

Wherein Y and Z can be represented by CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, orCF₃—C—CF₃. Similar to the dianhydride (e.g., AR1, AR2), the polyimidemay be composed of one or more diamines (AR3) or combinations of theabove structures. The resultant polyimides may be endcapped by a numberof chemicals know to the industry (e.g., phthalic anhydride) and thepolyimide or the polyamic acid precursor may be supplied in a variety ofsolvents known to those in the industry (e.g., N,N dimethylacetamide(DMAc), dimethyl foramide (DMF), N-methylpyrrolidinone (NMP)). Thehydrolytically stable polyimide may utilize mole ratios of thedianhydrides and may possess offsets (excess of diamine to dianhydride)similar to those known to the industry. The polyimides may also befurther modified by incorporating specialized constituents such ascrosslinking agents (e.g., nadic groups), fluorine containing groups(e.g., CF₃, SF₅, hexafluoropropane), or processing aids commonly knownto those in the industry. Examples of hydrolytically stable polyimidessuitable for embodiments of the present invention are:

-   -   1. LaRCT™ SI, wherein:        -   AR1: X is O (4,4′-oxydiphthalic anhydride, ODPA)        -   AR2: X is no element (3,4,3′,4′-biphenyltetracarboxylic            dianhydride, BPDA)        -   AR3: Z is O (3,4′-oxydianiline, ODA)    -   2. A polyimide described in NASA technical report #NAS        1.71:LAR-15109-1 (published Aug. 31, 1994), wherein:        -   AR1: X is O (4,4′-oxydiphthalic anhydride, ODPA)        -   AR2: X is C═O (3,3′,4,4′-benzophenonetetracarboxylic            dianhydride, BTDA)        -   AR3: Z is O (3,4′-oxydianiline, ODA)    -   3. A polyimide described in U.S. Pat. No. 5,171,828, wherein:        -   AR1: X is O (4,4′-oxydiphthalic anhydride, ODPA)        -   AR2: X is no element (3,4,3′,4′-biphenyltetracarboxylic            dianhydride, BPDA)        -   AR3: Y is O (4,4′-oxydianiline, (JDA)    -   4. LaRC™ TPI, wherein:        -   AR: X is C═0 (3,3′,4,4′-benzophenonetetracarboxylic            dianhydride, BTDA)        -   AR3: Z is C═0 (m-BDA)

FIG. 5 is a cross-sectional view of a coiled wire conductor forming amulti-filar conductor coil according to another embodiment of thepresent invention. The insulative layer 212 of hydrolytically stablepolyimide according to embodiments of the present invention can beutilized as a stand-alone insulation on a filer or as an initial layerof insulation followed by an additional outer layer as redundantinsulation to enhance reliability. For example, according to anembodiment of the present invention illustrated in FIG. 5, in additionto conductor wire 210 and insulative layer 212, one or more of theindividual coiled wire conductors 202A, 202B, 202C and 202D includes anadditional outer insulative layer 214, formed of known insulativematerials, such as ETFE, for example, to enhance reliability of thelead. According to the present invention, insulative layer 214 generallyhas a thickness T between approximately 0.0005 and 0.0025 inches, forexample, although other thickness ranges are contemplated by the presentinvention. Since the outermost insulative layer, i.e., insulative layer214, experiences more displacement during flex of lead 102 thaninsulative layer 212, it is desirable for insulative layer 214 to beformed of a lower flex modulus material than insulative layer 212, suchas ETFE.

By utilizing the insulative layer 212 of the present invention, thestimulating lead is reduced in diameter, and is more robust in regardsto mechanical flex and electrical insulation. The insulative layer 212provides an extremely long-term flex-life performance associated withthe ductility of the hydrolytically stable polyimide coating overconductor wires such as MP35N, used on conductor coils. These improvedproperties are related to the unique process of the multiple passapplication of the hydrolytically stable polyimide. The resultinginsulative layer 212 provides a highly reliable insulating andmechanically robust coating over implantable stimulating leads.

While an insulative layer formed only of ETFE tends to be susceptible tocreep, insulative layer 212 of the present invention, which is formed ofhydrolytically stable polyimide, is mechanically more robust,hydrolytically stable and possesses exceptionally dielectric properties,making the hydrolytically stable polyimide desirable for long-termimplant applications. The use of a thin layer of hydrolytically stablepolyimide coating on conventional MP35N alloy coil filars may also actas a protective barrier to reduce the incidence of metal inducedoxidation seen on some polyurethane medical device insulations.

FIG. 6 is a radial cross-section of an exemplary cabled wire conductoraccording to yet another embodiment of the present invention. FIG. 6illustrates cable 630 including bundled wire strands 632-637 formedabout a core wire strand 638, any or all of which strands may be formedfrom a Co—Ni—Cr—Mo alloy, MP35N, or any other conductivecorrosion-resistant and biocompatible material of sufficient strengthand toughness for incorporation into a medical electrical lead; adiameter of each wire strand in various embodiments is betweenapproximately 0.0005 inch and 0.005 inch. Using a conventional strandingmachine, wire strands 632-638 are each tightly bundled in a cable-likefashion; a lay or pitch of stranding is typically between 0.3 inch and0.6 inch. As is further illustrated in FIG. 6, cable 630 includes aninsulating layer 639 surrounding bundled wire strands 632-638, which isformed from a hydrolytically stable polyimide, examples of which havebeen previously described. It should be noted that, although FIG. 6illustrates insulating layer 639 surrounding the plurality of wirestrands as bundled, according to an alternate embodiment, one or more ofeach of the individual wire strands include an insulating layer of ahydrolytically stable polyimide, for example as illustrated in FIG. 4,and layer 639 may or may not be included. Another type of cableconfiguration, which may include a hydrolytically stable polyimideinsulating layer, is described in U.S. Pat. No. 5,760,341, issued toLaske et al., the teachings of which are incorporated herein.

According to one embodiment, layer 639 may be applied to the bundledwire strands 632-638 by passing them through a polyamic acid solutionand then heating the strands to a temperature sufficient to fullyimidize the polyimide; likewise layer 212 may be applied to conductor210 in a similar manner. As previously described, multiple coatingpasses may form layers 630 and 212. According to an alternate embodimentan extrusion process may be used to apply layer 639 or layer 212; thetype of polyimide described by Example 4, above, may be particularlysuitable for extrusion. According to yet another embodiment a secondlayer of another, insulative material is formed over layer 639, forexample a layer of ETFE as described in conjunction with FIG. 5.

While a particular embodiment of the present invention has been shownand described, modifications may be made. It is therefore intended inthe appended claims to cover all such changes and modifications, whichfall within the true spirit and scope of the invention.

1. A medical electrical lead, comprising a conductor including a layerof hydrolytically stable polyimide formed thereover; wherein thehydrolytically stable polyimide is defined by the following chemicalstructure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 2. The lead of claim 1, which is animplantable medical electrical lead.
 3. The lead of claim 1, wherein theconductor includes a plurality of bundled wire strands extending withinthe layer of hydrolytically stable polyimide.
 4. The lead of claim 1,wherein the conductor is one of a plurality of bundled wire strands. 5.The lead of claim 1, wherein the conductor is one of a plurality ofcoiled wire filars.
 6. The lead of claim 1, wherein the conductorcomprises a cable foamed by a bundle of wires.
 7. The lead of claim 1,wherein the conductor is a single wire filar.
 8. The lead of claim 1,wherein the conductor further includes a layer of fluoropolymer formedover the layer of hydrolytically stable polyimide.
 9. The lead of claim1 further comprising an insulative liner comprising PEEK or ETFE. 10.The lead of claim 1, wherein at least one AR is of the structure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 11. The lead of claim 1, wherein at least one AR₃ isrepresented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 12. The lead of claim 1, wherein the polyimide is preparedfrom 4,4′-oxydiphthalic anhydride, 3,4,3′,4′-biphenyltetracarboxylicdianhydride, and 3,4′-oxydianiline.
 13. An implantable medical devicecomprising the medical electrical lead of claim
 1. 14. A medicalelectrical lead, comprising a conductor including a layer of a polyimideformed thereover; wherein the polyimide is defined by the followingchemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 15. The lead of claim 14, which is animplantable medical electrical lead.
 16. The lead of claim 15, whereinthe polyimide is prepared from 4,4′-oxydiphthalic anhydride,3,4,3′,4′-biphenyltetracarboxylic dianhydride, and 3,4′-oxydianiline.17. The lead of claim 14, wherein the conductor includes a plurality ofbundled wire strands extending within the layer of polyimide.
 18. Thelead of claim 14, wherein the conductor is one of a plurality of bundledwire strands.
 19. The lead of claim 14, wherein the conductor is one ofa plurality of coiled wire filars.
 20. The lead of claim 14, wherein theconductor comprises a cable formed by a bundle of wires.
 21. The lead ofclaim 14, wherein the conductor is a single wire filar.
 22. The lead ofclaim 14, wherein the conductor further includes a layer offluoropolymer formed over the layer of polyimide.
 23. The lead of claim14 further comprising an insulative liner comprising ETFE or PEEK. 24.The lead of claim 14, wherein at least one AR is of the structure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 25. The lead of claim 14, wherein at least one AR₃ isrepresented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 26. An implantable medical device comprising the medicalelectrical lead of claim
 14. 27. A medical device electrical leadcomprising: a lead body extending from a proximal end to a distal endand having a connector assembly at the proximal end and electrodes atthe distal end; a multi-filar conductor coil extending through the leadbody between the proximal end connector assembly and the distal endelectrodes; and an insulative layer coupled to the multi-filar conductorcoil, the insulative layer comprising a polyimide material; wherein thepolyimide is defined by the following chemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 28. The lead of claim 27, wherein at leastone AR is of the structure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 29. The lead of claim 27, wherein at least one AR3 isrepresented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 30. The lead of claim 27, wherein the polyimide is preparedfrom 4,4′-oxydiphthalic anhydride, 3,4,3′,4′-biphenyltetracarboxylicdianhydride, and 3,4′-oxydianiline.
 31. The lead of claim 27, which isan implantable medical electrical lead.
 32. An implantable medicaldevice comprising the medical electrical lead of claim
 27. 33. A medicaldevice electrical lead comprising: a lead body extending from a proximalend to a distal end and having a connector assembly at the proximal endand electrodes at the distal end; a cable conductor extending throughthe lead body between the proximal end connector assembly and the distalend electrodes; and an insulative layer coupled to the cable conductor,the insulative layer comprising a polyimide material; wherein thepolyimide is defined by the following chemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 34. The lead of claim 33, wherein at leastone AR is of the structure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 35. The lead of claim 33, wherein at least one AR₃ isrepresented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 36. The lead of claim 33, wherein the polyimide is preparedfrom 4,4′-oxydiphthalic anhydride, 3,4,3′,4′-biphenyltetracarboxylicdianhydride, and 3,4′-oxydianiline.
 37. The lead of claim 33, which isan implantable medical electrical lead.
 38. An implantable medicaldevice comprising the medical electrical lead of claim
 33. 39. A medicalelectrical lead comprising: one or more conductors, each conductorsurrounded by an insulative layer comprising polyimide, wherein eachconductor is configured to perform one of therapy delivery and sensingof data associated with a patient; wherein the polyimide is defined bythe following chemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 40. The lead of claim 39, wherein at leastone AR is of the structure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 41. The lead of claim 39, wherein at least one AR₃ isrepresented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 42. The lead of claim 39, wherein the polyimide is preparedfrom 4,4′-oxydiphthalic anhydride, 3,4,3′,4′-biphenyltetracarboxylicdianhydride, and 3,4′-oxydianiline.
 43. The lead of claim 39, which isan implantable medical electrical lead.
 44. An implantable medicaldevice comprising the medical electrical lead of claim
 39. 45. A medicaldevice comprising an electrical lead comprising: a lead body extendingfrom a proximal end to a distal end and having a connector assembly atthe proximal end and electrodes at the distal end; and a plurality ofcoiled wire conductors extending through the lead body, each individualcoiled wire being surrounded by insulation, the plurality of coiled wireconductors disposed between the proximal end connector assembly and thedistal end electrodes; wherein the insulation surrounding eachindividual coiled wire comprises a polyimide material derived from oneor more aromatic dianhydrides and one or more aromatic diamines.
 46. Themedical device of claim 45, wherein the polyimide is prepared from4,4′-oxydiphthalic anhydride, 3,4,3′,4′-biphenyltetracarboxylicdianhydride, and 3,4′-oxydianiline.
 47. The medical device of claim 45,wherein the polyimide is defined by the following chemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 48. The medical device of claim 47, whereinat least one AR is of the structure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 49. The medical device of claim 47, wherein at least one AR₃ isrepresented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 50. The medical device of claim 45, wherein one or more ofthe plurality of conductors form a single circuit.
 51. The medicaldevice of claim 45, further comprising redundant insulation surroundingone or more individual coiled wires of the plurality of conductors. 52.The medical device of claim 51, wherein the redundant insulation isformed of a material having a flex modulus less than the insulationcomprising the polyimide material.
 53. The medical device of claim 45,wherein the plurality of coiled wire conductors forms a multi-filarconductor coil.
 54. The medical device of claim 45, wherein theplurality of coiled wire conductors form's a quadrafilar conductor coil.55. The medical device of claim 45, wherein the plurality of coiled wireconductors are parallel-wound in an interlaced manner to have a commonouter and inner coil diameter.
 56. The medical device of claim 45,further comprising an outer insulative sheath positioned about theplurality of coiled wire conductors.
 57. The medical device of claim 56,wherein the outer insulative sheath comprises a material selected fromthe group of polyurethane, silicone rubber, an ethylenetetrafluoroethylene (ETFE), and a polytetrafluoroethylene (PTFE). 58.The medical device of claim 45, wherein the coiled wire conductors forman internal lumen that further comprises an insulative liner, whereinthe insulative liner comprises a polymer selected from the group of afluoropolymer, a polyimide, and PEEK.
 59. The medical device of claim45, which is an implantable medical device.
 60. A medical devicecomprising an electrical lead comprising: a lead body extending from aproximal end to a distal end and having a connector assembly at theproximal end and a plurality of electrodes at the distal end; and aplurality of coiled wire conductors extending through the lead body anddisposed between the proximal end connector assembly and the distal endelectrodes, each coiled wire conductor being coupled to an electrode,and one or more individual coiled wire conductors being surrounded byinsulation; wherein the insulation comprises a first insulative layercomprising a polyimide material derived from one or more aromaticdianhydrides and one or more aromatic diamines, and a second insulativelayer having a lower flexural modulus than the first insulative layer.61. The medical device of claim 60, wherein the second insulative layercomprises an ethylene tetrafluoroethylene (ETFE).
 62. The medical deviceof claim 60, further comprising an outer insulative sheath positionedabout the plurality of coiled wire conductors.
 63. The medical device ofclaim 62, wherein the outer insulative sheath comprises a materialselected from the group of polyurethane, silicone rubber, an ethylenetetrafluoroethylene (ETFE), and a polytetrafluoroethylene (PTFE). 64.The medical device of claim 60, wherein the plurality of coiled wireconductors are parallel-wound in an interlaced manner to have a commonouter and inner coil diameter.
 65. The medical device of claim 64,wherein the coiled wire conductors form an internal lumen that furthercomprises an insulative liner, wherein the insulative liner comprises apolymer selected from the group of a fluoropolymer, a polyimide, andPEEK.
 66. The medical device of claim 60, wherein the polyimide isdefined by the following chemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 67. The medical device of claim 66, whereinat least one AR is of the structure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 68. The medical device of claim 66, wherein at least one AR₃ isrepresented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 69. The medical device of claim 60, which is an implantablemedical device.
 70. The medical device of claim 60, wherein thepolyimide is prepared from 4,4′-oxydiphthalic anhydride,3,4,3′,4′-biphenyltetracarboxylic dianhydride, and 3,4′-oxydianiline.71. A medical device, comprising: a housing including a connector block;a lead comprising a lead body extending from a proximal end to a distalend and including a connector assembly terminating at the proximal endand adapted to be coupled to the connector block of the housing; and aplurality of coiled wire conductors coupled to the connector assemblyand extending through the lead body, each individual coiled wireconductor being surrounded by insulation; wherein the plurality ofcoiled wire conductors are disposed between the proximal end and thedistal end; and wherein the insulation surrounding each individualcoiled wire conductor comprises at least a first insulative layercomprising a polyimide material derived from one or more aromaticdianhydrides and one or more aromatic diamines.
 72. The medical deviceof claim 71, further comprising a plurality of electrodes carried by thelead body, each coiled wire conductor being coupled to an electrode. 73.The medical device of claim 71, wherein the insulation further comprisesa second insulative layer comprising an ethylene tetrafluoroethylene(ETFE).
 74. The medical device of claim 71, wherein the lead furthercomprises an outer insulative sheath positioned about the plurality ofcoiled wire conductors.
 75. The medical device of claim 74, wherein theouter insulative sheath comprises a material selected from the group ofpolyurethane, silicone rubber, an ethylene tetrafluoroethylene (ETFE),and a polytetrafluoroethylene (PTFE).
 76. The medical device of claim71, wherein the plurality of coiled wire conductors are parallel-woundin an interlaced manner to have a common outer and inner coil diameter.77. The medical device of claim 76, wherein the coiled wire conductorsform an internal lumen that further comprises an insulative liner,wherein the insulative liner comprises a polymer selected from the groupof a fluoropolymer, a polyimide, and PEEK.
 78. The medical device ofclaim 71, wherein the polyimide is defined by the following chemicalstructure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 79. The medical device of claim 78, whereinat least one AR is of the structure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 80. The medical device of claim 78, wherein at least one AR₃ isrepresented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 81. The medical device of claim 71, wherein the polyimide isprepared from 4,4′-oxydiphthalic anhydride,3,4,3′,4′-biphenyltetracarboxylic dianhydride, and 3,4′-oxydianiline.82. The medical device of claim 71, which is an implantable medicaldevice.
 83. A medical device comprising an electrical lead comprising: alead body extending from a proximal end to a distal end and having aconnector assembly at the proximal end and electrodes at the distal end;a plurality of wire conductors extending through the lead body anddisposed between the proximal end connector assembly and the distal endelectrodes; and insulation surrounding the wire conductors, wherein theinsulation comprises a polyimide material derived from one or morearomatic dianhydrides and one or more aromatic diamines.
 84. The medicaldevice of claim 83, wherein the plurality of wire conductors forms aconductor coil.
 85. The medical device of claim 83, wherein theplurality of wire conductors forms a cable.
 86. The medical device ofclaim 83, wherein the insulation surrounds each individual wire of theplurality of wire conductors.
 87. The medical device of claim 83,wherein the polyimide is defined by the following chemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 88. The medical device of claim 87, whereinat least one AR is of the structure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 89. The medical device of claim 87, wherein at least one AR₃ isrepresented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 90. The medical device of claim 85, wherein the polyimide isprepared from 4,4′-oxydiphthalic anhydride,3,4,3′,4′-biphenyltetracarboxylic dianhydride, and 3,4′-oxydianiline.91. The medical device of claim 85, which is an implantable medicaldevice.
 92. An implantable medical device comprising: a lead bodyextending from a proximal end to a distal end; a plurality of conductorsextending between the proximal end and the distal end of the lead body;and a single insulative layer positioned about each of the plurality ofconductors, wherein the insulative layer is formed of an aromaticpolyimide of the following structure:

wherein AR comprises one or more aromatic groups, each pair of carbonylgroups is attached to adjacent carbon atoms in a ring of AR, and atleast one AR₃ is represented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 93. The device of claim 92, wherein at least one AR is of thestructure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 94. The device of claim 92, wherein the polyimide is preparedfrom 4,4′-oxydiphthalic anhydride, 3,4,3′,4′-biphenyltetracarboxylicdianhydride, and 3,4′-oxydianiline.
 95. An implantable medical devicecomprising: a housing generating electrical signals for deliveringtherapy, the housing having a connector block; a lead having a lead bodyextending from a proximal end to a distal end, the proximal end of thelead body being insertable within the connector block and electricallycoupling the housing and the lead; a plurality of conductors extendingbetween the proximal end and the distal end of the lead body; and aninsulative layer positioned about the plurality of conductors, whereinthe insulative layer is formed of an aromatic polyimide of the followingstructure:

wherein AR comprises one or more aromatic groups, each pair of carbonylgroups is attached to adjacent carbon atoms in a ring of AR, and atleast one AR₃ is represented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 96. The device of claim 95, wherein at least one AR is of thestructure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 97. The device of claim 95, wherein the polyimide is preparedfrom 4,4′-oxydiphthalic anhydride, 3,4,3′,4′-biphenyltetracarboxylicdianhydride, and 3,4′-oxydianiline.
 98. A medical electrical leadcomprising: a conductor including a single insulative layer of anaromatic polyimide having the following structure:

wherein AR comprises one or more aromatic groups, each pair of carbonylgroups is attached to adjacent carbon atoms in a ring of AR, and atleast one AR₃ is represented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 99. The lead of claim 98, wherein at least one AR is of thestructure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 100. The device of claim 99, wherein the polyimide is preparedfrom 4,4′-oxydiphthalic anhydride, 3,4,3′,4′-biphenyltetracarboxylicdianhydride, and 3,4′-oxydianiline.
 101. A medical device comprising onat least some portion thereof a polyimide of the structure:

wherein AR comprises one or more aromatic groups, each pair of carbonylgroups is attached to adjacent carbon atoms in a ring of AR, and atleast one AR₃ is represented by one of

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.
 102. The device of claim 101, wherein at least one AR is ofthe structure:

wherein X is one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, CF₃—C—CF₃, or noelement.
 103. The device of claim 101, wherein the polyimide is preparedfrom 4,4′-oxydiphthalic anhydride, 3,4,3′,4′-biphenyltetracarboxylicdianhydride, and 3,4′-oxydianiline.
 104. A method for manufacturing amedical electrical lead, the method comprising the steps of applying toan elongate lead conductor a liquid comprising a polyamic acid precursorand forming a layer of hydrolytically stable polyimide on the elongatelead conductor; wherein the hydrolytically stable polyimide is definedby the following chemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 105. A method for manufacturing a medicalelectrical lead, the method comprising the steps of applying to anelongate lead conductor a liquid comprising a polyamic acid precursorand forming a layer of a polyimide on the elongate lead conductor;wherein the polyimide is defined by the following chemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 106. A method for manufacturing a medicalelectrical lead, the method comprising the steps of applying to anelongate lead conductor a liquid comprising a polyamic acid precursorand forming a layer of hydrolytically stable polyimide on the elongatelead conductor; wherein the hydrolytically stable polyimide is definedby the following chemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 107. A method for manufacturing a medicalelectrical lead, the method comprising the steps of applying to anelongate lead conductor a liquid comprising a polyamic acid precursorand forming a layer of a polyimide on the elongate lead conductor;wherein the polyimide is defined by the following chemical structure:

wherein AR is derived from one or more dianhydrides and AR₃ is derivedfrom one or more diamines.
 108. A method for manufacturing a medicaldevice, the method comprising the step of forming on at least someportion of the device a layer of aromatic polyimide of the structure:

wherein AR comprises one or more aromatic groups, each pair of carbonylgroups is attached to adjacent carbon atoms in a ring of AR, and AR₃ isrepresented by one of:

wherein Y and Z are one of CH₂, CH₃—C—CH₃, O, C═O, S, SO₂, andCF₃—C—CF₃.